1. Field of Invention
This invention relates to the preparation of elasticized composite structures which can be used as or converted into components of disposable hygiene products such as diapers. These composite structures are elasticized using polyurethane films or filaments to impart stretchability to the structures so prepared. A selected type of polyurethane or polyurethaneurea is extended to a relatively high draft and, in its stretched condition, is adhesively bonded to at least one relatively inelastic substrate with hot melt adhesive applied at relatively high temperature. The stretched polyurethane/substrate combination is then allowed to relax and retract to thereby provide an elasticized gathered or puckered stretchable composite which can provide stretchable components for use in disposable diapers or other disposable hygiene products or for use in articles of apparel.
2. Summary of the Related Technology
The use of elastomeric fibers, filaments and/or films in, for example, leg bands and other components of disposable diapers has been known for many years. In a typical process to produce these components, spandex fibers or filaments or natural or synthetic rubber film strips are elongated to a specific draft and adhesively attached to, for example, one or two layers of a nonwoven substrate using a hot melt adhesive. This provides good stretch and recovery properties to the diaper component, e.g., the nonwoven substrate, which has been elasticized by incorporation of the elastomeric fibers, filaments and/or film into or onto this component.
The adhesives used in this process are frequently those which must be heated to an elevated temperature in order to form a good bond between the elastomeric fiber, filament or film and the material of the diaper component being elasticized, for instance a nonwoven fabric or substrate. At this elevated temperature, the break tenacity of the elastomeric fiber, filament or film is significantly lower than its break tenacity at room temperature (˜75° F.). If the break tenacity of the elastomeric fiber, filament or film at the elevated temperature experienced at the point of contact with the hot melt adhesive is lower than the first load force of the fiber, filament or film at room temperature and at the draft used in the elasticizing process, then the fiber, filament or film will break. It is thus commonly known that if the elastomeric fiber, filament or film is stretched to too great an extent or if the adhesive is heated to too high a temperature when it contacts the elastomer, excessive instances of breaks in the elastomeric fibers, filaments or film will occur during the process of preparing elasticized material for hygiene product components.
Typical process conditions for elasticizing material for diaper components with spandex and a hot melt adhesive involve use of a spandex fiber at a draft between 3.5 and 4.5 (250% to 350% elongation) and a standard elastic attachment hot melt adhesive temperature of about 260° F. to 325° F. (127° C. to 177° C.) when the adhesive is applied by a spiral spray process. If the spandex elongation is increased beyond 4.5 when the hot adhesive is applied, instances of breaks in the spandex at the point of adhesive application rapidly increase to an unacceptable level. If the adhesive temperature is decreased below about 260° F. (127° C.) to lessen the thermal load on the spandex fiber, the integrity of the bond between the spandex and the diaper component, e.g., nonwoven, decreases to an unacceptable level.
Breaks in the elastomeric fibers, filaments or film in the production of elasticized structures used for components of disposable hygiene products are highly undesirable. This is because when the elastomer breaks, the disposable product production line must be shut down; the elasticizing fibers, filaments or film must be re-strung; and the apparatus restarted. This causes significant down time, for example, of a diaper production line and generates a number of waste diapers.
Notwithstanding the availability of components for disposable hygiene products which have been elasticized by the adhesive attachment of spandex, it would be advantageous to identify selected combinations of materials (e.g., certain spandex materials and hot melt adhesives) and procedures for preparation of composite structures used for such components, which permit higher draft (elongation) of the spandex elasticizing material with minimized occurrence of spandex breaks upon contact of the spandex elasticizing agent with hot melt adhesives. Stretching spandex to greater elongation in turn would permit the use of less spandex to elasticize a given number of components, thereby minimizing costs. Alternatively, elongation of the high draft potential spandex only to an extent which is close to that used in conventional elasticizing procedures would permit the effective use of hot melt adhesives under conditions which induce fewer instances of breaks in the spandex, thereby also providing a reduced cost procedure.